1. Field of Invention
This invention relates to using explosive forces generated inside a contained environment to subject materials to extremely high pressure. Examples include a process of breaking apart cellulose fibers and the removal of lignin in connection with the wood pulp industry and the hardening of materials, such as metals.
2. Description of Related Art
Currently the wood pulp industry uses chemical steam processing and mechanical grinding and milling to break apart cellulose fibers and remove lignin. These processes use an excess of energy, can take a long period of time, and use environmentally unfriendly chemicals.
Chemically produced pulps are processed in digesters by a sulfite or kraft process. Digesters can be designed for batch or continuous flow.
The sulfite pulping mechanism utilizes the raw materials sulfurous acid and either sodium, magnesium, or calcium bisulfate as the two main ingredients to process the lignin within the wood chips. The sulfurous acid works as a catalyst and breaks the ether linkages in the lignin molecule. Then, the sulfite ions bond to the open sites on the lignin molecules to aid in the lignin dissolution. A high temperature and long cook time are required for these reactions to have successful rates and yields. Normal operating conditions for batch sulfite pulping include a digester temperature of 150.degree. C. with a cook time of four hours.
One problem with the sulfite mechanism is that the sulfurous acid acts on the carbohydrates in the fiber. The more carbohydrates that are lost, the weaker the pulp becomes and the weaker the resulting dried paper product will be. The sulfite cook actually leaves about 4% of the original lignin in the chip to reduce the chance of losing any extra carbohydrates.
The kraft pulping method eliminates the need for sulfurous acid as a raw material. Instead, the raw materials are sodium hydroxide and sodium sulfide. Sodium sulfide can double the rate of delignification over the sulfite process; hence the kraft process is the dominant process in the industry. The mechanics of kraft reactions are similar to those of sulfite reactions. In this case, the OH-ions from the sodium hydroxide will break the lignin ether linkages. Once broken, the hydrosulfide ions (SH--) can bond with the open lignin sites to react with methyl groups and form methyl mercaptans. Methyl mercaptans contribute to the unique odor associated with kraft pulping.
The kraft pulping process leaves more lignin with the digested pulp than the sulfite process. The main reason for this is that the OH--ions can more easily penetrate the crystalline cellulose walls and break down the carbohydrates than can the sulfurous acid ions. Usually about 8% of the original lignin stays with the chips.
During the past decade, the paper industry has seen a significant increase in the percentage of secondary fibers used to make up the paper machine furnish (secondary fibers=OCC--old corrugated containers, MOW--mixed office waste, etc.). In fact, almost all newsprint and an increasing number of tissue and medium board machines are going to 100% recycled fibers for their funish.
A problem most mills encounter when changing over to recycled fibers from a virgin chemically pulped furnish is a reduction in fiber strength and size. When a mill decides to implement a recycled fiber program, a new recycled fiber plant is usually constructed in order to repulp the recycled products and to remove undesirable contaminants that are introduced to the system from the recycled materials (i.e. latexes, coatings, inks, glues, waxes, oils, etc.). These contaminants can destroy a mills production rate if not efficiently removed in the recycling plant. Hence, a successful recycle fiber plant will take previously made papers and boxes and efficiently deliver to the paper machines the cleanest and strongest pulp possible. The characteristics of each batch of recycled pulp will have a dramatic effect on the efficiency of the paper machines.
Fibers that have already been used to make a box or piece of paper are inherently weaker than virgin fibers. These fibers have already been subjected to refining, high temperature dryer cans, press loading, etc., which take away from their size and strength. The main way to strengthen a recycled fiber is to re-swell and then mechanically refine the fiber. The swelling is done with water and pH control (wood fibers-are hydrophilic and will accept water). Once the fibers are swollen they can be refined in order to fibrillate the fibers. Fibrillation is when a single fiber is subjected to mechanical forces that cause fibrils to branch off of the original fiber. This action will increase the surface area of the fiber, which will form a stronger mat on the paper machine wire. Swelling and refining also help open up the hydroxyl sites on the fiber and fibrils, which increases the chance of hydrogen bonding between the fibers. Hydrogen bonding is essential for a strong finished sheet of paper.
U.S. Pat. Nos. 5,273,766 and 5,328,403 disclose a tank for tenderizing meat in which the meat is supported along a hemispherical wall of the tank and then subjected to a shock wave produced by an explosive charge. The tank disclosed in these two patents is specifically hemispherical in shape and therefore the amount of meat processed by the tank per explosive charge is limited to the amount of meat that can be supported along the hemispherical wall of the tank. To increase the amount of meat processed per explosive charge, the radius of the hemisphere that defines the shape of the tank must be increased, greatly increasing the volume of water required to fill the tank. It is well known that for a given surface area a sphere has the greatest volume of any shape.